KR101482478B1 - Si based negative electrode material - Google Patents

Abstract

In the present invention, the composition formula is Si _a Sn _b Ni _c Ti _y M _m C _z wherein a, b, c, y, m and z are atomic% values, M is at least one of Fe, And a lithium ion battery having a relationship of a> 0, b> 0, z> 0, y≥0, 0≤m≤1, c> 5, z + 0.5b> a and c + y> And a negative electrode active material. The method for preparing the active material comprises the steps of: - providing a mixture of powders of elements and / or alloyed powders of these elements of the composition Si _a Sn _b Ni _c Ti _y M _m C _z , and - And high-energy pulverization.

Description

Si based negative electrode material {SI BASED NEGATIVE ELECTRODE MATERIAL}

The present invention relates to an anode active material for a lithium ion battery and a method of manufacturing the same.

Portable electronic devices are becoming smaller, lighter, and often require more energy. As a result, interest in high capacity and compact batteries is increasing. Non-aqueous electrolyte lithium ion batteries are considered to be one of the most promising technologies for this application. Lithium is added to the active material during the lithiation reaction, and lithium ions are removed from the active material during the delithiation reaction. Most of the anodes that are currently applied to lithium ion batteries are acted upon by lithium intercalation and de-intercalation mechanisms during charging and discharging. Examples of such materials include graphite and lithium titanium oxide (LTO). However, these active anode materials lack gravimetric capacity and volumetric capacity. The weighing capacities of graphite and LTO are 372 mAh / g (LiC ₆ ) and 175 mAh / g (Li ₄ Ti ₅ O ₁₂ ), respectively.

Another group of active materials act by alloying and de-alloying a metal, a metal alloy or a composite metal alloy with lithium. The term metal may refer to both metals and metalloids. Some good examples are pure silicon, pure tin or amorphous CoSn alloys (commercialized as Nexelion by Sony). Problems associated with the application of lithium alloy type electrodes are mainly related to the continuous expansion and reduction of the particle volume or are caused by unwanted phase changes during cycling. Repeated expansion and contraction of the particle volume can result in contact loss between the particles and the current collector, decomposition due to repetitive exposure of the electrolyte to new particle surfaces upon volume change, pulverization of particles due to internal stress, Or cracking. ≪ RTI ID = 0.0 > Phase change also affects long-term cycling. After the lithium substitution reaction from pure silicon to Li ₁₅ Si ₄ phase, cycling is no longer reversible. Also, after the depolymerization reaction during long-term cycling, the presence or formation of a crystalline glass tin phase instead of the tin-transition metal alloy phase results in a decrease in capacity.

It is an object of the present invention to provide a negative electrode material for a nonaqueous electrolyte secondary battery having a large capacity and a long cycling life.

The present invention is characterized in that the composition formula is Si _a Sn _b Ni _c Ti _y M _m C _z wherein a, b, c, m, y and z represent atomic% Co, and c + y> 0.75. B, where a> 0, b> 0, z> 0, y≥0, c> 5, 0≤m≤1, A negative electrode active material for a lithium ion battery. In one embodiment, y > 0. In another embodiment, the Si content is defined as 0 < In another embodiment, z > a. The active substance may theoretically have a volume increase rate of less than 200% upon charging. In one embodiment, 99% or more of the cathode material is Si _a Sn _b Ni _c Ti _y C _z where a> 0, b> 0, z> 0, y> 0, c> 5, b> a and c + y> 0.75 · b). In another embodiment, the negative active material for a lithium ion battery has a composition formula of Si _a Sn _b Ni _c M _y C _z wherein a, b, c, y and z represent atomic% values, M is Ti, a 0, b> 0, z> 0, y? 0, c> 5, z + 0.5? B> a and c + y> 0.75? B.

According to a second aspect of the present invention,

- providing a mixture of elements in the composition Si _a Sn _b Ni _c Ti _y M _m C _z and / or an alloyed powder of these elements, and

- high energy milling of the powder mixture under non-oxidizing conditions, to produce a negative electrode active material as described above. In one embodiment, the composition is Si _a Sn _b Ni _c M _y C _z , where M is Ti.

In one embodiment, the high energy pulverization is performed in a protective atmosphere of a gas comprising any one or more of Ar, N ₂ , CO and CO ₂ . In another embodiment, the high energy pulverization is carried out in a protective atmosphere of a gas consisting of any one or more of Ar, N ₂ , CO and CO ₂ . In another embodiment, the high energy pulverization is performed in a horizontal or vertical attritor. In yet another embodiment, Sn and Ni are provided as an atomicized SnNi alloy, preferably an atomized brittle SnNi alloy and any one or more of a Ni ₃ Sn ₄ compound, preferably an atomized Ni ₃ Sn ₄ compound. In another embodiment, Sn, Ti and Ni are provided as atomized Ni ₃ Sn ₄ -Ti alloys. C may be provided as carbon black. The method described above may further comprise the step of adding conductive carbon or graphite to the high energy pulverized mixture.

It is appropriate to mention in WO 2007/120347 that the electrode composition Si _a Sn _b M _y C _z , wherein M may be Ti, a + b> 2y + z is disclosed. When expressed in terms of the composition of the present application (Si _a Sn _b Ni _c Ti _y C _z ), this means that a + b> 2. (C + y) + z . However, in the present application, since z + 0.5 · b> a and c + y> 0.75 · b, This also implies z + 0.75 · b> a + 0.25 · b; c + y> 0.75 · b, which implies that z + c + y> a + 0.25 · b; Which is equal to z + c + y + 0.75 · b> a + b; (Again c + y &gt; 0.75 · b) and a + b <2 · (c + y) + z . The negative effects of increasing amounts of both Si and Sn in WO 2007/120347 are discussed below.

US2010-0270497 discloses an alloy of the type Si _a Sn _b C _c Al _d M _e , where M is, for example, Ni, Fe or Cu. However, it has been found that the presence of Al in the present application negatively affects the capacity retention of the active material. In addition, for Si _a Sn _b C _c M _e compositions meeting the requirement that M = Ni and a + b + c + e = 1 and additional limitations (defined in claim 1 of the present application) It is not. In the present application, z + 0.5 · b> a, or even z> a, is true for all alloys containing Ni in US 2010-0270497. This means that the content of Si in the present application can be reduced and an anode composition excellent in capacity retention can be obtained. Therefore, problems associated with volumetric expansion during battery charging are avoided.

1 is an X-ray diffraction pattern of a Si-Sn-Ni-Al-C alloy (Comparative Example 1).
2 is an X-ray diffraction pattern of a Si-Sn-Ni-C alloy.
3 is an X-ray diffraction pattern of a Si-Sn-Ni-Ti-C alloy.
Figure 4 shows the capacity (mAh / g) versus number of cycles (N) of active material for the alloys described in the examples.

The present inventors have found that when the composition formula is Si _a Sn _b Ni _c Ti _y M _m C _z wherein a, b, c, y, m and z represent atomic% values, in this case a + b + c + + z = 100). &lt; / RTI &gt; In one embodiment, M is at least one element selected from the group consisting of iron, chromium, and cobalt. These elements are usually found as impurities in the alloy after the milling process. Also, a> 0, b> 0, z> 0, y? 0, 0? M? 1, c> 5, z + 0.5? B> a and c + y> 0.75?

Silicon is used to increase the capacity in the active material since its weight capacity is about 3570 mAh / g. In one embodiment, the silicon is present in the alloy composition in an amount up to 45 atomic%. A large amount of silicon in the active material can increase the amount of volumetric expansion, since such an amount of expansion must be buffered in the final cathode to an unattainable level, resulting in power failure and premature failure of the battery.

Silicon exists as very small crystalline or semi-crystalline particles. This is because the battery can be used as an end use after being &quot; conditioned &quot; in the initial charge and discharge stages. During this conditioning step, a very low potential (0 mV to 30 mV) is applied relative to the lithium reference electrode, making the crystalline silicon partially amorphous. Different material conditioning steps may be required to obtain higher crystallinity. After conditioning the silicon during normal operation, a higher potential is used to introduce stable cycling. If (after conditioning) when the silicon is cycling at a low voltage compared to the lithium reference electrode during operation of the electrode Li ₁₅ Si _4, there can be different forms, this Li ₁₅ Si ₄ phase would not be available for longer reversible cycling. Depending on the amount and type of electrolyte or electrolyte additive, typical cycling after conditioning can be limited to about 45 mV to 80 mV compared to the metal lithium reference electrode.

Tin is used in alloys because of its high electrochemical capacity and excellent conductivity. High levels of tin increase the rate of lithium substitution and improve the performance of the active material, but the formation of elemental tin should be prevented. Instead of a more reversible electrochemical tin-transition metal alloy phase during the lithium-to-lithium reaction, larger free crystalline tin particles may also be formed and grow. Therefore, it is provided to form a small stable irreversible tin alloy particle.

The composite anode active material according to the present invention includes nickel. Nickel is added as a metal binder between tin and the less conductive metalloid silicon. Grinding or handling of ductile tin is also improved by alloying with nickel. To improve grinding, it may be convenient to start with a brittle intermetallic compound, for example a Ni ₃ Sn ₄ alloy instead of a pure nickel metal. In certain embodiments, other elements may be added to enhance the cyclability of the alloy compound. Such a metal or metalloid may be added together with nickel. When titanium is added, the titanium also acts as a grain refiner.

In the production method of the present invention, conductive carbon is added to act as a lubricant which enhances conductivity when cyclizing the active material and prevents contact loss between particles and contact with the current collector. When the content of silicon and tin is high, an increased amount of carbon may be added to improve the milling process. The BET of the conductive carbon (e.g., C-Nergy 65 (Timcal), commercially available) is greater than 50 m 2 / g, which leads to an increase in the irreversible capacity. BET is significantly reduced in function of grinding time and parameters, however, BET increases when natural or synthetic graphite is used during grinding. Small amounts of silicon carbide can be formed during milling (which may or may not be formed) ), Because silicon in the silicon carbide is not alloyed with Li and the specific capacity of the powder is reduced.

Nickel and titanium (if present) are added in sufficient amounts to the tin content to form an intermetallic phase that combines with all of the tin to optimize the cycle characteristics of the tin phase. In one embodiment, the sum of atomic percent, c + y, is greater than 0.75 · b. In addition, in other embodiments, the total amount of tin phase and carbon in the milling step is sufficient to allow for the expansion of the silicon in the conductive matrix of the active anode powder, such feature being z + 0.5 · b> a or z> a Lt; / RTI &gt; is satisfied.

In one embodiment, excess graphite or conductive carbon may be added to the Si _a Sn _b Ni _c Ti _y M _m C _z active material during electrode production. The carbon-containing compound helps buffer the expansion of the material and maintains the conducting properties of the finished electrode. To prepare the cathode, the active material can be mixed with a conductive additive as well as with a suitable binder. This binder enhances the integrity of the finished composite electrode, e. G., Adhesion to the current collector, and contributes to cushioning the continuous expansion and reduction of the volume. A number of suitable binders are described in the literature. Most of these binders are n-methyl-pyrrolidone or water based. Usable binders include, but are not limited to, polyimide, polytetrafluoroethylene, polyethylene oxide, polyacrylate or polyacrylic acid, cellulose and polyvinyl difluoride.

The electrolyte used in the battery enables the action of the active material. For example, a stable solid-electrolyte interface phase (SEI) is formed that protects the silicon interface. Electrolyte additives such as VC, FEC or other fluorocarbonates form a stable and flexible SEI barrier that allows lithium diffusion and prevents decomposition of the electrolyte. If the SEI layer is not flexible, for example, the continuous expansion of the silicon containing particles induces a continuous decomposition of the electrolyte at the silicon surface. The electrolyte may also be in the form of a solid or gel.

The invention is further illustrated through the following examples.

An example  One

The Ni ₃ Sn ₄ powder, Si powder, Al powder and carbon (C- energy 65, timkal) was ground in a horizontal Saba liter (from a simol of ZOZ (Simoloyer) ^® cm01, benden material). In order to prevent oxidation, milling was carried out under an argon gas atmosphere. The composition and process conditions are given in Table 1. The values for the composition parameters a, b, c, y (where Ti is replaced by Al in the general formula) and z are given in Table 8.

Experimental conditions of the counterexample 1 Remarks amount Ni ₃ Sn ₄ Manufactured in the laboratory 47.29 g Si Keyvest Si 0 탆 to 50 탆 12.53 g Al Merck 808 K3696756 1.40 g Carbon black Timal C-Energy 65 7.43 g Total powder 68.65g ball Diameter 5 mm, hardened steel 100 Cr6 1373 g BPR (ball / powder) 20 Chargeability mill 38 vol% Grinding time (hours) 20 hours Rotational speed (rpm) 700rpm

After milling, the powder was passivated under controlled flow to prevent excessive oxidation. The powder properties are given in Table 3 and the XRD is shown in Fig. 1 (all XRD plots show the counts per second for 2 &amp;thetas;). The composite anode was prepared using 55 wt% powdered powder, 25 wt% Na-CMC binder (MW &lt; 200 K), and 20 wt% inducible additive (C-energy 65, Timal). 4 wt% Na-CMC binder aqueous solution was prepared and then mixed overnight. Conductive carbon was added and then mixed with the binder solution under high shear. After the carbon was dissolved, the active material was added. The paste was allowed to sit and then coated on a copper foil (17 mu m) with a wet thickness of 120 mu m to 230 mu m. The electrode was dried overnight.

The rounded electrodes were punched and dried using a vacuum at over 100 &lt; 0 &gt; C. The electrode was electrochemically tested for metal lithium using a coin cell fabricated in a glove box (dry Ar atmosphere). The electrochemical evaluation of the different alloys was carried out in a half-coin cell (using metal lithium as the corresponding electrode). The first two cycles were performed at a slow rate (C / 20 rate, which means that the chargeability or discharge rate within 20 hours of the active material is 1 Ah / g) and the cut- The cut-off voltage was 0V, the cut-off voltage in the second cycle was 10mV, and the cut-off voltage in the pre-lithium step in both the first cycle and the second cycle was 2V. The third cycle and the fourth cycle were carried out at a C-rate, i.e. C / 10 (meaning that the chargeability or discharge rate in 10 hours of the active material was 1 h / g) The off-state voltage was 70 mV, and the cut-off voltage in the pre-lithium reaction stage was 2 V. This cut-off voltage was kept the same for the rest of the test period.

The subsequent 48 cycles were then carried out at a higher rate (1C ratio, which means that the filling rate or discharge rate within 1 hour of the active material is 1 Ah / g). To evaluate the remaining capacity of the battery, the 54th cycle and the 55th cycle were performed again at a slower rate (C / 10). From then on, alternating cycles of rapid cycling (1C) for 48 cycles and slow cycling (C / 10) for 2 cycles (rapid cycling 48 times, slow cycling 2 times, fast cycling 48 times, slow cycling 2 Etc.). This method enabled the rapid and reliable electrochemical evaluation of alloys.

Table 1a provides details regarding the cycling sequence.

[Table 1a]

(Valid for all embodiments)

The electrochemical results for Comparative Example 1 are shown in FIG. 4 (presented in terms of the capacity per cycle). On the graph, the indicated points are the second cycle, the fourth cycle, and the second cycle (i.e., the second cycle, the fourth cycle, the 55th cycle, the 106th cycle, the 157th cycle , The 208th cycle, the 259th cycle, and the 310th cycle). It can be confirmed that the capacity of the Al-containing material is gradually decreased upon cycling.

Example  2 (y = 0)

Ni ₃ Sn ₄ in the powder was ground, 1400rpm for 8 hours in the Si powder and the level of carbon black Saba liter (from a simol of ZOZ ^® cm01, benden material). In order to prevent oxidation, milling was carried out under an argon gas atmosphere. The composition and process conditions are given in Table 2. Values for composition parameters a, b, c, and z are given in Table 8.

Experimental conditions of Example 2 Remarks amount Ni ₃ Sn ₄ Manufactured in the laboratory 44.85 g Si Key Vest Si 0 탆 to 50 탆 14.13 g Carbon black Timal C-Energy 65 8.52 g Total powder 67.5 g ball Diameter 5 mm, hardened steel 100 Cr6 1350 g BPR (ball / powder) 20 Chargeability mill 38 vol% Grinding time (h) 8 hours Rotational speed (rpm) 1400rpm

After milling, the powder was passivated under controlled flow to prevent excessive oxidation. Powder characteristics are given in Table 3, and XRD is shown in Fig.

Additional fabrication and coin cell fabrication was performed as in Example 1. Electrochemical results are shown in Fig. Capacity retention during cycling was superior to that of the counter case 1.

The properties of the powders prepared in Examples 1 and 2 Counterfeit 1 Example 2 Particle size d50 (占 퐉) 3.79 5.40 Oxygen content (wt%) 2.0% 1.7% BET (m &lt; 2 &gt; / g) 18.00 5.75 Theoretical capacity (mAh / g) 1201 1200 Second cycle capacity (mAh / g) C / 20 - 10mV 1074 1112 Fourth cycle capacity (mAh / g) C / 10 - 70mV 847 863 106th cycle capacity (mAh / g) C / 10 - 70mV 758 (90%) 831 (96%) 208th cycle capacity (mAh / g) C / 10 - 70mV 647 (76%) 724 (84%) 310 cycle capacity (mAh / g) C / 10 - 70mV 539 (64%) 597 (69%)

In the above table (and also in Table 7 below), the capacities for the second cycle, the fourth cycle, the 106th cycle, the 208th cycle and the 310th cycle are given for each alloy, and the corresponding capacity retention (C / 10, cut-off voltage is 70 mV).

Example  3

Ni ₃ Sn ₄ powder was pulverized by a Si powder, the Ti powder and 1400rpm for 8 hours carbon black in the horizontal Saba liter (from ^® cm01, benden material to simol of ZOZ). In order to prevent oxidation, milling was carried out under an argon gas atmosphere. The composition and process conditions are given in Table 4. Values for the composition parameters a, b, c, y, and z are given in Table 8.

Experimental conditions of Example 3 Remarks amount Ni ₃ Sn ₄ Manufactured in the laboratory 50.75g Si Key Vest Si 0 탆 to 50 탆 15.81 g Ti Spherical powder, 100 mesh, Aldrich, 2.00 g Carbon black Timal C-Energy 65 9.50g Total powder 78.06g ball Diameter 5 mm, hardened steel 100 Cr6 1600 g BPR (ball / powder) 20 Chargeability mill 44 vol% Grinding time (hours) 8 hours Rotational speed (rpm) 1400rpm

After milling, the powder was passivated under controlled flow to prevent excessive oxidation. The powder properties are given in Table 7.

Additional fabrication and coin cell fabrication was performed as in Example 1. Electrochemical results are shown in Fig. The capacity retention during cycling was superior to that of Example 1 and Example 2.

Example  4

Ni ₃ Sn ₄ powder was pulverized by a Si powder, the Ti powder and 1400rpm for 8 hours carbon black in the horizontal Saba liter (from ^® cm01, benden material to simol of ZOZ). In order to prevent oxidation, milling was carried out under an argon gas atmosphere. The composition and process conditions are given in Table 5. Values for the composition parameters a, b, c, y, and z are given in Table 8.

Experimental conditions of Example 4 Remarks amount Ni ₃ Sn ₄ Manufactured in the laboratory 50.75g Si Key Vest Si 0 탆 to 50 탆 15.81 g Ti Spherical powder, 100 mesh, Aldrich 4.00 g Carbon black Timal C-Energy 65 9.50g Total powder 80.06g ball Diameter 5 mm, hardened steel 100 Cr6 1600 g BPR (ball / powder) 20 Chargeability mill 44 vol% Grinding time (hours) 8 hours Rotational speed (rpm) 1400rpm

After milling, the powder was passivated under controlled flow to prevent excessive oxidation. Powder characteristics are given in Table 7, and XRD is shown in FIG.

Additional fabrication and coin cell fabrication was performed as in Example 1. Electrochemical results are shown in Fig. The capacity retention during cycling was superior to that of Example 1 and Example 2.

Example  5

Ni ₃ Sn ₄ powder was pulverized by a Si powder, the Ti powder and 1400rpm for 8 hours carbon black in the horizontal Saba liter (from ^® cm01, benden material to simol of ZOZ). In order to prevent oxidation, milling was carried out under an argon gas atmosphere. The composition and process conditions are given in Table 6. Values for the composition parameters a, b, c, y, and z are given in Table 8.

Experimental conditions of Example 5 Remarks amount Ni ₃ Sn ₄ Manufactured in the laboratory 50.75g Si Key Vest Si 0 탆 to 50 탆 15.81 g Ti Spherical powder, 100 mesh, Aldrich 6.00 g Carbon black Timal C-Energy 65 9.50g Total powder 82.06g ball Diameter 5 mm, hardened steel 100 Cr6 1600 g BPR (ball / powder) 20 Chargeability mill 44 vol% Grinding time (hours) 8 hours Rotational speed (rpm) 1400rpm

After milling, the powder was passivated under controlled flow to prevent excessive oxidation. The powder properties are given in Table 7.

Additional fabrication and coin cell fabrication was performed as in Example 1. Electrochemical results are shown in Fig. The capacity retention during cycling was superior to that of Example 1 and Example 2.

The properties of the powders prepared in Examples 3 to 5 Example 3 Example 4 Example 5 Particle size d50 (占 퐉) 5.43 5.38 5.3 Oxygen content (wt%) 1.6% 1.8% 1.8% BET (m &lt; 2 &gt; / g) 7.5 6.4 5.8 Theoretical capacity (mAh / g) 1190 1161 1132 Second cycle capacity (mAh / g) C / 20 - 10mV 1060 1020 923 Fourth cycle capacity (mAh / g) C / 10 - 70mV 819 798 709 106th cycle capacity (mAh / g) C / 10 - 70mV 802 (98%) 815 (102%) 719 (102%) 208th cycle capacity (mAh / g) C / 10 - 70mV 727 (89%) 724 (91%) 652 (92%) 310 cycle capacity (mAh / g) C / 10 - 70mV 630 (77%) 648 (81%) 560 (79%)

Composition parameter values of the powders prepared in Examples 1 to 5 At% a (Si) b (Sn) c (Ni) y z (C) Counterfeit 1 29.0% 16.0% 12.0% Al: 3% 40.0% Example 2 29.6% 16.2% 12.2% 0.0% 42.0% Example 3 29.0% 16.1% 12.0% Ti: 2.2% 40.7% Example 4 28.4% 15.7% 11.8% Ti: 4.2% 39.9% Example 5 27.8% 15.4% 11.6% Ti: 6.2% 39.1%

In certain embodiments of the present invention, 25? A? 35, 10? B? 20, 10? C? 15, 1? Y? 10 and 35? Specific examples may be 25? A? 30, 15? B? 18, 10? C? 12.5, 2? Y? 8 and 37? Z? 43. In all experiments, any one or more of Fe, Co and Cr could be identified in trace amounts due to the grinding apparatus (0 &lt; = m &lt; = 1). However, the m-values are not taken into account in the analysis results of Table 8.

Claims (13)

A, b, c, y, m and z are atomic% values, M is at least one of Fe, Cr and Co, and the composition formula is Si _a Sn _b Ni _c Ti _y M _m C _z , 15, 1? Y? 10, 35? Z? 45, 0? M? 1, z + 0.5? B> a, c + y> 0.75 Negative active material for a lithium ion battery.
The method according to claim 1,
30, 15? B? 18, 10? C? 12.5, 2? Y? 8 and 37? Z? 43. 3. The method according to claim 1 or 2,
and y is 3 at% to 12 at%. - providing a mixture of powders of elements in the composition Si _a Sn _b Ni _c Ti _y M _m C _z and / or a mixture of alloyed powders of these elements, and
A method for producing the negative electrode active material according to any one of claims 1 to 3, comprising a step of high-energy pulverizing the powder mixture under non-oxidizing conditions. 5. The method of claim 4,
Wherein the high energy pulverization is performed in a protective atmosphere of a gas containing any one or more of Ar, N ₂ , CO and CO ₂ . 5. The method of claim 4,
Wherein the high energy pulverization is performed in a horizontal or vertical attritor. 5. The method of claim 4,
Wherein Sn and Ni are provided as any one or more of atomized SnNi alloy and Ni ₃ Sn ₄ compound. 5. The method of claim 4,
Sn, Ti and Ni are provided as atomized Ni ₃ Sn ₄ -Ti alloys. 5. The method of claim 4,
And C is provided as carbon black. 5. The method of claim 4,
Further comprising the step of adding conductive carbon or graphite to the high energy pulverized mixture. delete delete delete

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